Method of making electric coils



JM 13, 1948 J. T. osTERMAN ETAL 2,434,511

METHOD OF MAKING ELECTRIC COILS Filed Oct. 7, 1944 @M4 @dal ATTORNEYPatentedjlan. 13, 1,1948

METHOD OF MAKING ELECTRIC COILS Joseph T. Osterman,

, Ericksberg, American Northampton, and Alvah 0. Springfield, Mass.,assignors to Bosch Corporation,

Springfield,

' Mass., a corporation of New York Application October 7, 1944, SerialNo. 557,710

oolaims. (oies-155.57) L The present invention relates to methods ofmaking electric coils on heat-resistant coll forms with wire terminalsrigidly fastening the coil winding to the form, by bonding the end turnsof the winding to separated conducting areas baked on the form. Suchcoils employ relatively ne wire and are used generally as for instancein sparkplugs in ignition systems of the capacitor discharge type.electrical instruments, and radio and other high frequency devices.

Heretofore it was customary to solder the ends of the coil winding toconducting areas or bands character.

strains. Preferably also the conducting areas onv the coil formconstitute end bands of ysuch width as will be'covered vby a number ofturns of bare wireof the size used, so as to secure rigid terminalsofuniform and permanent electrical Preferably also the same metallicmaterial is used for producing the conducting areas on the form and' forbonding the winding ,to those areas, since such subsequent bonding lmaythenk be accomplished at a temperature,

lower than is required to produce the conducting areas withv themetallic material then penetratsometimes baked on coil forms to producethe' v coil terminals, butgthis subjected the form to heat shocks ofsuch nature as often fractured it particularly if silver solder wasused, or set up such stresses and strains as resulted in unduly fragileforms which broke upon ordinary mechan ical shock orvibration. Also, theelectric contact between the wire and the conducting areas occurred atspots only, and the surface of the wire at the joints often corroded insoldering and sometimes'further thereafter so as to be faulty andnon-uniform' in resistance upon completion besides deteriorating duringservice. Also the solder sometimes formed `lumps and otherwise lackeduniformity in dimensions, which detracted from the smooth and regulardimensions of the terminal in such wise as to prgvent reliable contacttherewith in electrical devices and circuits.

, Furthermore, in application to sparkplugs in f which the coils wereimpregnated'in place at comparatively high temperature and also inservice reached a comparatively high temperature at the location ofy thecoil, the solder would sometimes melt and thereupon interrupt theelectrical circuit at one or both terminals of the coil.

In accordance with our invention, the foregoing difllculties areobviated by bonding the bare end turns of the coll winding to theconducting areas .on the coil form by baking adher-v ent metallicmaterial spread over at least a substantial part of the contactingsurfaces of the winding while the endturns thereof are held against theconducting areas. In order to wind closely, insulated wire is usedpreferably, and to ing the coil form. .After the winding is bonded tothe' conducting areas to form the coil terminals,` it is preferable toadherently coat the terminals' with lhighly conducting material tothereby increase the electric conductivity thereof.

In such colis. the coil4 form is preferably cylindrical so as to takeadvantage of the reduced nection between the withstand the baking andoperating temperatures this insulation is of the heat-resistant type.Preferably the bonding operation, and also the operation of baking theconducting areas on the coil form, are accomplished by gradually heatingthe coil form to the necessary temperature and thereafter graduallycooling it to room temperature, thereby avoiding the subjection of thecoil form to heat shocks and to excessive stresses and cost of cuttingthe forms into lengths from a long tube. However, in case a springterminal is' required at one end of the coil to compensate for changesin dimensions in the device incorporatingl the coil, the form may havean integral cross wall to which the spring is riveted. In this lattercase the outer face of the crossr wall is likewise coated with adherentmetallicI material at the time the conducting areas are formed on theouter surface of the form, and the cross wall is likewise coatedwith thehighly conductive ma terial, to thereby produce a good electrical conendof the coll winding and the spring.

Accordingly, one object of the invention is to provide methods ofproducing electric coils having rigid terminals which are smooth and ofsubstantially uniform dimensions and of` uniformv and permanentelectrical characteristics.

Another object is to provide such methods as are applicable to the rapidand uniform production in quantity of inexpensive coils of this kind.

These and other objects and advantages of the invention will beunderstood from the following description of two embodiments herein,using as t asseoir 3 at each end bared for bonding to the conductingbands; Fig. 4 shows the coil of Fig. 3 after its completion, the endturns of the winding being connected to the conducting bands by means ofadherent metallic material appropriately baked to mechanically andelectrically secure the winding to the conducting bands to form rigidterminals therewith, and the terminals being covered with a layer ofcopper applied thereto by electrolytic deposition or spraying: F18. 5 isan enlarged detail oi a completed terminal of Fig. 4; and Fig. 8 shows amodified form of coil of this type provided with a spring terminal.

Referring to the embodiment of Figs. 15 the tubular coil form I consistspreferably of suitable ceramic material as porcelain, such as that usedin sparkplug insulators. Preferably, in order to reduce their cost, theforms are cut from long tubes while plastic before firing. the cornersat I of each form being rounded on by turning or grinding. After thefired coil form. as shown in Fig. 1, is thoroughly cleansed with carbontetrachloride to remove oil. grease and other foreign materialtherefrom, each of its ends is coated by l stenciling or in any othersuitable way, with a band of commercial metallic paint consisting of 90%silver and. 10% platinum. Each band is of sufilcient width to underlie'about i0-15 turns of wire subsequently wound on the coil form almostfrom end to end thereof. These bands are then baked on the coil form bygradually raising its temperature in a furnace to a value between 1000F. and 1100 F. durins a period of about 3 to 5 minutes. Then the coilform is gradually cooled to room temperature. Thus in these steps ofprocessing, the coil form is not subjected to such heat shock, eitherwhile the temperature is being increased or decreased, as might crack orbreak it or might produce such stresses and strains therein as wouldcause its fracture upon ordinary mechanical shocks or vibration, and thepaint is baked into the exterior pores of the ceramic and completelyaround the coil form, and if desired around its end surfaces also, insharply defined bands l of continuously conducting metal ofsubstantially uniform width and thickness.

Instead of using porcelain, other heat-resistant coil forms, as steatiteor glass-bonded mica may be used. Furthermore, the metallic band may bein the form of a paste and may contain pure silver or pure platinum orpure gold or other suitable adherent metallic materials includingadmixtures thereof such that after the baking operation `there is noformation of metal oxide having a relatively high electrical resistance.

Having the finished coil form with conducting end bands thereon, asshown in Fig. 2, relatively small copper wire 4 of a B and S gagebetween No. and No. 42 having a bare diameter of about 10 mils down toabout 2.5 mils. is wound thereon substantially from end tofend oi' thecoll form as shown in Fig. 3. Preferably the wire is covered with a wellknown insulation which is a ceramic (inorganic) insulating coating oncopper, nickel and other types of wire and which may contain resin andwhich is heat-resistant capable of withstanding without change atemperature of at least 800 F. Other insulation materials havingsuitable heat resisting characteristics may be used if desired. About 10to l5 turns at each end of the winding I depending upon the size of wiremaking lup about the width of the bands 3, are bared of its insulationin any suitable way as by scraping. The bare end turns B are then givena coating of paint, preferably of the same'oomposition as the adherentmetallic material of the end bands I. While these coated turns are helddown tightly against the bands 8 by spring clips or tape. and thewinding I on that portion of the coil form therebetween maintainedtight, the wire-wound coilA form is baked in a furnace at agraduallyincreasing temperature up to about 500 F. during a period of 3to 5 minutes. and then gradually cooled. to bond the end turns i of thewinding to the bands l. The spring clips or tapes are then removed. Thistemperature of about 500' F., instead of the baking temperature ofbetween 1000 F. and 1100 Il'. for the bands 8. suiiices for the bondingoperation between the end turns I and bands I because the first coatingof paint requires a higher temperature for penetration of the ceramicwhile the second coating of paint does not require such penetration butmerely a bond between two contact surfaces. Either before or after thewound coil form has its temperature from the second baking operationgradually reduced to the room temperature. a second and heavier coatingl of the same paint may preferably be baked over the bonded end turns ata gradually rising temperature nnally reaching about 500' l". after aperiod of 2 to 21/2 hours. This additional coating assists in producinga terminal 1 in which the end turns are rigidly secured to the band in abond of comparatively low electrical resistance capable of withstandinga temperature in service of at least 600 F. Whether or not theadditional coating is applied. the terminals may then, if desired, befurther covered by electrolytically plating them with copper, silver orother highly conducting metal I which does not melt at the temperatureto which the coil is subjected in service, or by spraying them withsuitable metal. to thereby further reduce the electrical resistance ofthe terminals. Whether or not the step of electrolytical deposition orspraying is used. each of the termi. nais 1 so produced is smooth allaround its outer surface and of uniform dimensions, comprising asubstantially continuous bond between 10-15 short-clrcuited end turns ofthe winding. Also, such terminals and windings made in quantity havesubstantially uniform electrical resistance and result in coils ofsubstantially uniform distributed inductance and capacity. Also theterminals are mechanically rigid and not only are non-corroded whencompleted but do not corrode thereafter in such wise as would materiallychange the electrical resistance thereof. Furthermore, due to thegradual application of heat and gradual reduction in temperature. thecoil form is not so apt to be cracked or broken under stresses andstrains such as may result in fracture under ordinary mechanical shockor vibration in handling or service. 4

In the modincation shown in Fig. 6, the ooil form l has near one end anintegral cross wall il which is perforated at I l. whereas the remainderof the coil form is tubular as before. The bond between the bared endturns of the winding and the end bands or conducting areas are formed asbefore. but the initial coating of adherent metallic material isextended over the inner surface.

. form, preferably after the winding is secured in place, with its endsconnected to the conducting area on the cross wall by a brass rivet Il.Buch a coil, with a spring electrically connected toone terminalthereof. is useful in mounting in devices,

such as sparkplugs, having mounting dimensions which are variable withinthe `compensation afforded by the spring I 3. Obviously, this electriccoil has the mechanical and electrical characteristics of the embodimentof Figs. 1-5.

It will be apparent that in either of the embodiments of Figs. 1-5 orFig. 6, the wire of the coil may be bare instead of insulated, the turnst then being maintained in spaced relation in the well known way as byforming in the coil form a helical groove in which the wire is wound.'This and other changes and modifications may be made withoutdepartingfromthe spirit of the invention as embodied within the broadterms of the appended claims.

paint on separated areas on the coil form, heat-4 ing the paint to atemperature between substantially 1000 F. and 1 100 F. during a periodof Having thus described our invention, what we claim is:

1. The method of making an electric coil hav- `ing terminals and aheat-resistant inorganic coil form, which consists in spreading anadherent metallic material on separated areas on the coil form, heatingthe metallic material to a temperstufe at which it `is baked on the coilferm to produce conducting areas thereon, winding wire on the coil formover the conducting areas and the portion therebetween, covering atleast a part of the surface of the bare end turns of the winding with acoating of an adherent metallic material, and baking the metallicmaterial on the end turns while in contact with the conducting areas tothereby bond the metallic materials into coil terminals rigidlyfastening the winding to the coil form.

2. The method of making an electric coil havwinding wire on the coilform over the conducting about 3 to 5 minutes to bake the paint on thecoil form and produce conducting areas thereon,

areas and the portion therebetween, covering at least a part of thesurface of the bare end turns of the winding with a coating ofplatinum-silver paint, and bakingthe .paint on the end turns while incontact with the conducting areas at a temperature of substantially 500F. to thereby bond the metallic materials on the end turns and theconducting areas into coil terminals rigidly fastening the coil to thecoil form.

6. The method of making an electric coil having terminals and aheat-resistant inorganic coil form, which consists in spreadingplatinum-silver ing terminals and a heat-resistant inorganic coil form,which consists in spreading an adherent metallic material on separatedareas on the coil form, heating the metallic material to a temperatureat which it is baked on the coil form to produce conducting areasthereon', `winding wire on the coil form over the conducting areas andthe portion therebetween, covering at least a part of the surface of thebare end turns of the winding with a coating of an adherent metallicmaterial, baking the metallic material on the end turnswhile in contactwith the conducting areas to thereby bond the metallic materials intocoil terminals, spreading a layer of adherent metallic material over thecoil terminals to embed the end turns, and baking said layer to bond itonto the terminals. y

3. The method of making an electric coil having terminalsv and aheat-resistant inorganic form, which consists in forming bands 'ofanadpaint on separate areas onlthe coil form, heating the paint to atemperature between substantially 1000 F. and 1l00 F. during a period ofabout 3 to 5 minutes to bake the paint on the coil form and produceconducting areas thereon, winding l wire on the coil form over theconducting areas herent metallic material at the ends of the coil Aform, heating the metallic material `to a temperature at which it isbaked on the coil form to produce conducting bands thereon, winding wireon the coil form over the end bands and the portion therebetween,covering the entire surface of the bare end turns of the winding with acoating of an adherent metallic material, and baking the metallicmaterial on the end turns while in contact Awith the conducting bands tothereby bond the metallic materials into coil terminals rigidlyfastening the coil to the coil form.'

4. The method of, making an electric coil having terminals and a'heat-resistant inorganic coil form, which consists in coating anadherent metallic material on separated areas on lthe coil form, heatingthe metallic material to a tem'- perature at which it is baked on thecoil form to produce conducting areas thereon, winding wire on the coilform over the conducting areas and the portion therebetween, covering atleast a part of the surface of the bare end turns of the winding with acoating of platinum-silver paint, baking the paint on the end turnswhile in contacts with the conducting areas at a temperature ofsubstantially 500 F. .during a period of about 3 to 5 minutes to therebybond the metallic materials of the paint into coil terminals, spread'-'ing a Ilayer of platinum-silver paint over the terminals, baking saidlayer at atemperature of substantially 500 F. fora period of about 2 to21/2 hours, and thereafter cooling the coll to thereby rigidlytfastenthe winding to the coil terminals.

7. The method of making an electric coil having terminals and aheat-resistant inorganic coil form, which consists in spreading anadherent metallic material on separated areas on the coil form, heatingthe metallic' material to a temper,- aturel at which it is baked on thecoil form to produce conducting areas thereon, winding wire on the coilform over the conducting areas and the portiontherebetween covering atleast apart of the surface of the bare end turns of the winding with acoating of an adherent metallic material, baking the metallic materialon the' endr turns while in' contact with the conducting areas tothereby bond the metallic material into terminals rigidly fastening thewinding to the coil form, and adherently coating a layer of highlyconductive material on the terminals to increase' the conductivitythereof.

8. .The method of making an electric coil having terminals and aheat-resistant inorganic coil form, which consists in forming bands ofan adhercnt metallic material near the ends of the coil rorm,'heatingthe metallic material to a temperature at which it is baked on the coilform to 7 produce conducting bands thereon. winding heatresistantinsulated wire on the coil form over the conducting bands and theportion therebetween, baring the end turns of the. winding of theinsulation thereon, covering at least a part of the `surface of the bareend turns of the coil with an adherent metallic'material, baking themetallic material on the end turns while in contact with the conductingbands to thereby bond the metallic materials into coil terminala rigidlyfastening the coil to the coil form, and depositing a coating ofconducting material thereover by electrolytically plating the terminalawith high conductive material to increase the conductivity thereof.

9. The method of making`an electric coil having one rigid terminal andone resilient terminal and also having a heat-resistant inorganic coilform of tubular section with an inner cross wall, which consists inspreading an adherent metallic material near one end oi' the coil formand also spreading adherent metallic material in a continuous mass overthe other end of the coil form and over the cross wall, heating themetallic A material to a temperature at which it is baked 8 on the coilform to produce conducting areas thereon. winding wire over the outersurface of the coil form and over the conducting areas and the portiontherebetween, covering at least a part of the surface of the bare endturns of the winding with a coating of an adherent metallic material,baking the metallic material on the end turns while in contact with theconducting areal to thereby bond the metallic materials into coilterminala rigidly fastening the coil to the ooil form, and fastening aresilient terminal to the croaa wall in contact with the conducting areathereon.

JOSEPH T. OBTERMAN. ALVAH 0. ERI.

REFERENCES CITED The following references are of record in the ille ofthis patenti l UNITED STATES PATENTS Number Name Date 2,075,515 FisherMax'. 30. 1037 1,871,371 Jackson Aug. 9, i932 Schellenger Nov. 5, 1985

